JP3632676B2 - Fuel cell system and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell system and a control method thereof, and more particularly, to a fuel cell system in which gas replacement in a fuel gas circulation pipe is improved and a control method thereof in a fuel cell system in which fuel gas is recirculated by an ejector.
[0002]
[Prior art]
A fuel cell is a device that directly generates electricity by electrochemically reacting hydrogen and oxygen by supplying a fuel gas containing hydrogen to the fuel electrode and supplying air containing oxygen to the air electrode. High power generation efficiency can be obtained even on a scale, and the environment is excellent.
[0003]
In recent years, the use of solid polymer ion-exchange membranes as electrolytes has enabled a reduction in size and output, and solid polymer fuel cells that do not require acid aqueous solutions have attracted attention as a fuel cell system using hydrogen gas. Has been.
[0004]
In a fuel cell, a fuel gas containing hydrogen and air containing oxygen are supplied to a fuel electrode and an air electrode, which are opposed to each other with a solid polymer film interposed therebetween. In order to reduce the consumption of raw fuel gas in this fuel cell and to improve the output characteristics by reducing the utilization rate of hydrogen gas, the exhaust gas from the fuel electrode of the fuel cell is recirculated and externally supplied. Many recirculation systems have been devised which are mixed with newly supplied hydrogen-rich fuel gas and supplied to the fuel electrode of the fuel cell.
[0005]
It is known that the power generation efficiency of a fuel cell is improved by keeping the amount of exhausted fuel gas to be recirculated and the amount of fuel gas newly supplied from the outside at a certain ratio or more. As a circulation device that mixes two flows, an ejector that uses negative pressure and dragging depending on the flow rate of the supplied fuel gas is used.
[0006]
An example of a fuel cell system that circulates fuel gas using an ejector is disclosed in Japanese Patent Application Laid-Open No. 10-511497. According to this prior art, the ejector is used as a pump that connects the fuel gas inlet pipe and the fuel gas circulation pipe and circulates the remaining fuel gas that has not been consumed in the fuel cell stack to the stack inlet again. .
[0007]
[Problems to be solved by the invention]
In the above fuel cell, at the time of start-up, fuel gas and air are first supplied to the fuel cell so that sufficient reaction gas is distributed to all anodes (fuel electrodes) and cathodes (oxidant electrodes), and electric power can be taken out. It is necessary to.
[0008]
However, in the case of a conventional fuel cell system having a circulation system, even if sufficient fuel gas is distributed in the fuel gas passage in the stack, if the fuel circulation pipe is not sufficiently replaced with fuel gas, the output of Immediately after starting the extraction, the impure gas (gas with a low hydrogen concentration) remaining in the fuel circulation pipe flows into the vicinity of the anode, and the fuel voltage is not sufficiently supplied to the electrode reaction surface. Since it may drop rapidly, there is a problem that it takes a long time (start-up time) until output is possible at start-up.
[0009]
In view of the above problems, an object of the present invention is to provide a fuel cell system and a control method thereof that can shorten the startup time by quickly replacing the fuel circulation pipe with fuel gas when the fuel cell system is started. Is to provide.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention supplies unreacted fuel gas discharged from the fuel electrode outlet of the fuel cell stack to the suction port of the first ejector via the fuel gas circulation pipe, and is driven to the inlet of the first ejector. In the fuel cell system, a new fuel gas is supplied as a flow, and a mixed gas of the unreacted fuel gas and the new fuel gas is supplied from the outlet of the first ejector to the fuel cell stack. And a switching means for selectively switching whether or not to use the second ejector, and at the time of starting the fuel cell system, the second ejector is connected to the suction port of the second ejector. The gist is to switch the switching means to use.
[0011]
【The invention's effect】
According to the present invention, by using the negative pressure generated by the second ejector using the air discharged from the fuel cell stack as the driving force, the residual gas in the fuel gas circulation piping section is sucked, so that the fuel gas circulation The inside of the piping part can be quickly replaced with fuel gas, and the start-up time can be shortened.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
[First Embodiment]
FIG. 1 is a configuration diagram showing the configuration of the first embodiment of the fuel cell system according to the present invention.
[0013]
Air is supplied through an air inlet pipe 9 by an air supply device 2 installed on the air electrode inlet side of the fuel cell stack 1 in which fuel cells are stacked. An air exhaust pressure control valve 7 is installed on the air electrode outlet side, whereby the stack air inlet pressure can be controlled to a desired value.
[0014]
Fuel gas is supplied by a fuel gas supply device 3 installed on the fuel electrode inlet side of the fuel cell stack 1. Immediately after the fuel gas supply device 3, a fuel gas shut valve 4 is installed to interrupt the fuel gas. A fuel gas supply pressure regulating valve 5 is installed downstream thereof, and a fuel gas circulation ejector 6 (first ejector) is installed downstream thereof and connected to the fuel gas inlet pipe 11.
[0015]
The fuel gas supply pressure adjustment valve 5 can control the stack inlet fuel gas pressure to a desired value. The fuel gas from the fuel electrode outlet is returned to the suction portion of the fuel gas circulation ejector 6 through the fuel gas circulation pipe 14.
[0016]
A purge valve 8 is installed in the vicinity of the stack outlet of the fuel gas circulation pipe 14 and is opened when water clogging occurs. Water clogging can be eliminated by temporarily increasing the flow rate of the fuel gas. The pipe end of the purge valve 8 is connected downstream of the air exhaust pressure control valve 7 and is diluted with air before being discharged to the outside.
[0017]
Here, the inlet of the fuel gas replacement acceleration ejector 16 (second ejector), which is a feature of the present invention, is connected via the check valve 18 immediately before (upstream) the air exhaust pressure regulating valve 7, and its outlet is air. The exhaust pressure control valve 7 is connected downstream.
[0018]
At the suction part (suction port) of the fuel gas replacement promotion ejector 16, a replacement promotion pipe 19 branched from the fuel gas circulation pipe 14 immediately before the suction part entrance of the fuel gas circulation ejector 6 is provided with a replacement promotion shut valve 17 (switching means). : First on-off valve).
[0019]
In the fuel cell system configured as described above, at the time of start-up, the control device 24 supplies fuel gas and air to the fuel electrode and the air electrode, respectively, and also opens the replacement promoting shut valve 17 and is generated by the fuel gas replacement promoting ejector 16. Residual gas inside the fuel gas circulation pipe 14 is sucked out by the negative pressure, and the replacement with the fuel gas in the pipe is promoted.
[0020]
FIG. 2 is a flowchart for explaining the gas replacement operation at the time of startup.
When power is supplied to the fuel cell system, the control device 24 checks sensors and actuators (not shown) in the fuel cell system, and when the fuel gas and air can be supplied, the start of the present invention is started. Enter the sequence.
[0021]
In Step 10, first, the replacement promoting shut valve 17 is closed and the purge valve 8 is opened, and then the supply of fuel gas and air is started at a predetermined flow rate. At this time, the fuel gas supply pressure control valve 5 and the air exhaust pressure control valve 7 are controlled by the controller 24 so that both the gas pressures of the fuel gas and the air at the stack inlet become Ps.
This is an operation for discharging liquid water condensed and accumulated in the stack or the pipe.
[0022]
In step S12, it is determined whether the elapsed time of the timer started at the start of gas supply has elapsed t1 seconds, and the process does not proceed to the next step until t1 seconds elapse (until the condensed water discharge is completed).
In the next step S14, the shut valve 17 is opened, the purge valve 8 is closed, and the fuel gas pipe replacement promoting operation is started.
[0023]
In step S16, it is determined whether or not the stack inlet pressure may exceed the set value Ps for a certain time t2 seconds. If so, the process proceeds to step S18, and if not, the process proceeds to step S20.
When the process proceeds to step S18, it is determined that if the flow rate is kept at the set value, the pressure exceeds the set value, and the purge valve 8 is also opened to prevent the pressure from becoming excessive.
In step S20, if the purge valve 8 is closed, the purge valve 8 is operated as it is. If the purge valve 8 is opened, the purge valve 8 is operated so as to be closed.
[0024]
Thereafter, when the process proceeds to step S22, it is determined whether or not the elapsed time of the timer has exceeded t3 seconds and the stack voltage V has reached Vs (the voltage at which the cell voltage can be regarded as an average rise), and the condition is satisfied. If so, the process returns to the next step S24, and if not, the process returns to step S16.
[0025]
In step S24, the shut valve 17 is closed and, at the same time, the purge valve 8 is also closed. Thus, normal fuel gas circulation is started.
In step S26, load extraction is started, and a normal operation sequence is started.
In addition, t3 of step S22 may be a constant or may be changed depending on the driving situation.
[0026]
For example, the determination time t3 may be lengthened according to the stop duration before starting. This is because if the stop duration is short, the hydrogen used in the previous operation remains in the fuel gas circulation pipe, so the time required for hydrogen replacement can be short. Therefore, the start-up time can be minimized by shifting to the normal operation sequence as quickly as possible in the replacement promotion operation. FIG. 3 is a graph showing an example of the determination time t3 in step S22 with respect to the stop time before activation.
[0027]
Further, in the case of a system that performs idle stop control that temporarily stops power generation at low loads, t3 is set to a certain length (about 10 seconds) during normal startup, and t3 = 0 during restart after idle stop. It is good to do. This is because even when restarting after an idle stop, hydrogen remains in the fuel gas circulation pipe, so there is no problem even if power is taken out immediately. Therefore, even if the idle stop control is performed in the present embodiment, the start time for restarting by the idle stop is not extended meaninglessly.
[0028]
In this embodiment, the stack inlet pressure is controlled so as to keep the set value Ps during the replacement promotion operation (when the replacement promotion ejector is in use). It is better if the pressure is higher than that at the time of start-up that is not used (for example, 120% of normal idle power generation).
By increasing the supply pressure, the supply flow rate of the fuel gas can be increased and the replacement time can be further shortened.
[0029]
In addition to the above control, when water clogging occurs in the fuel gas passage in the stack, the purge valve 8 can be opened and the fuel gas replacement promoting ejector 16 can be used.
[0030]
When the purge valve 8 is activated due to the occurrence of water clogging, the fuel gas replacement acceleration ejector 16 may be used at all times. If it is determined that the amount of water clogging is large, or even if the purge valve 8 is opened, the clogging will be eliminated. The fuel gas replacement accelerating ejector 16 may be used only when it does not progress.
[0031]
FIG. 4 is a flowchart for explaining the water clogging operation in the present embodiment, and is configured as a routine executed by the control device 24 at regular intervals, for example.
[0032]
In FIG. 4, it is first determined in step S30 whether water clogging has occurred. If water clogging has not occurred, the process proceeds to step S32, the purge valve 8 and the shut valve 17 are closed, and the process is terminated.
[0033]
If it is determined in step S30 that water clogging has occurred, the process moves to step S34 to determine whether water clogging is large. If there is a large amount of water, that is, the process proceeds to step S36, the purge valve 8 and the shut valve 17 are opened, and the process is terminated.
[0034]
If it is determined in step S34 that the amount of water, that is, the amount is small, the process proceeds to step S38 and the purge valve 8 is opened. Next, in step S40, it is determined whether or not a predetermined time has elapsed since the purge valve 8 was opened. If the predetermined time has not elapsed, the process is terminated. If it is determined in step S40 that a predetermined time has elapsed since the purge valve 8 was opened, the shut valve 17 is opened in step S42 and the process is terminated.
[0035]
It should be noted that whether or not water clogging has occurred in step S30 can be determined from the voltage of each cell of the fuel cell. In this case, an increase in the fuel gas flow rate is made larger than when only the purge valve 8 is used, so that it becomes possible to cope with an abrupt cell voltage drop due to a large amount of water clogging that could not be met in time only with the purge valve. The emergency stop can be avoided and the drivability can be improved.
[0036]
On the other hand, even when power generation is stopped, power generation continues for a while due to residual hydrogen in the fuel electrode even after the fuel supply shut-off valve 4 is closed. There is no problem because it is possible to effectively use this power generation to charge the storage battery at normal times, but if you want to stop the power generation as soon as possible due to some abnormal situation, the fuel gas replacement promotion ejector separate from the above control By using 16, the residual gas can be discharged to the outside at an early stage and power generation can be stopped reliably at an early stage. At this time, the time can be further shortened by opening the purge valve 8.
[0037]
At this time, by fully opening the air exhaust pressure control valve 7, it is possible to avoid damaging the membrane due to excessive differential pressure between the air electrode and the fuel electrode.
[0038]
FIG. 5 is a flowchart for explaining the operation at the time of emergency stop in the present embodiment. First, it is determined in step S50 whether or not it is an emergency stop. If it is not an emergency stop but a normal stop, the process proceeds to step S52, where the shut valve 4 is closed and the process ends. If it is an emergency stop, the process proceeds to step S54, the shut valve 4 is closed, the purge valve 8 and the shut valve 17 are opened, and the process is ended.
[0039]
As described above, according to the present embodiment, at the time of start-up, using the negative pressure generated by the fuel gas replacement acceleration ejector using the supplied air as the driving force, the residual gas in the fuel gas circulation piping section is sucked out and quickly It is possible to replace it with fuel gas, and it is possible to shorten the start-up time and start the start-up without sufficiently replacing the residual gas in the fuel gas circulation pipe, thereby avoiding deterioration of a specific cell. .
[0040]
Further, the inlet of the fuel gas replacement promotion ejector 16 is connected to the upstream of the air exhaust pressure regulating valve 7 via the check valve 18, and the outlet thereof is connected downstream of the air exhaust pressure control valve 7. Since the differential pressure can be increased, the suction effect by the fuel gas replacement promotion ejector 16 is great, and the backflow from the fuel gas replacement promotion ejector side to the air exhaust pressure control valve side can also be prevented.
[0041]
Further, since whether or not to use the fuel gas replacement promoting ejector 16 is switched by opening and closing the replacement promoting shut valve 17, it is possible to switch only by operating one valve, and when the fuel gas replacement promoting ejector is not used, the fuel is replaced. Since the suction port of the gas replacement promoting ejector is completely blocked, there is no interference with the suction action of the fuel gas circulation ejector.
[0042]
[Second Embodiment]
FIG. 6 is a configuration diagram showing the configuration of the second embodiment of the fuel cell system according to the present invention. In the present embodiment, in contrast to the first embodiment of FIG. 1, the circulation shut-off shut valve 21 (second on-off valve 21) is located in the vicinity of the inlet of the circulation ejector suction portion where the replacement promoting pipe 19 branches and further near the circulation ejector suction portion. ) Is added. Other configurations are the same as those in FIG.
[0043]
In the present embodiment, when the gas replacement inside the fuel gas circulation pipe 14 is promoted, the circulation shut-off shut valve 21 is controlled to be closed, and during normal operation, the circulation shut-off shut valve 21 is controlled to open. Accordingly, the residual gas is not sucked into the fuel gas circulation ejector 6 and mixed into the stack, so that the replacement with the fuel gas in the fuel gas circulation pipe 14 can be promoted more quickly.
[0044]
FIG. 7 is a flowchart for explaining the startup operation in the second embodiment. In contrast to the flowchart of FIG. 2 of the first embodiment, in FIG. 7, in step S60, the circulation shut-off shut valve 21 is closed simultaneously with the shut valve 17, and in step S62, the circulation shut-off shut valve 21 is opened and then the shut valve 17 is closed. Only thing is different. Other operations are completely the same, and the same step number is assigned to the same step, and the duplicate description is omitted.
[0045]
FIG. 8 is a configuration diagram showing the configuration of the third embodiment of the fuel cell system according to the present invention. In this embodiment, with respect to the first and second embodiments, there is a branch pipe (air introduction pipe) between the air supply device 2 and the stack 1, and the air introduction shut valve 22 (third on-off valve) and the second one. The stack inlet fuel gas pipe 11 is connected via a check valve 23. Other configurations are the same as those of the second embodiment of FIG.
[0046]
FIG. 9 is a flowchart for explaining a system stop operation in the third embodiment.
First, in step S80, after the gas supply is stopped, the fuel supply shut valve 4 is closed, the air introduction shut valve 22 is opened, and air is supplied at a predetermined flow rate. At this time, the circulation shutoff shut valve 21 is closed, and the shut valve 17 and the purge valve 8 are opened. Then, the fuel gas supply pressure adjustment valve 5 and the air exhaust pressure control valve 7 are controlled so that the stack inlet pressure becomes the predetermined pressure Ps ′ at the time of stop. Next, in step S82, the process waits until the elapsed time from the start of stop exceeds t4. When the elapsed time exceeds t4, the process proceeds to step S84 and the system is shut down.
[0047]
In this embodiment, by supplying air also to the fuel electrode inlet of the stack at the time of stoppage, the unreacted gas in the fuel gas pipe including the inside of the stack is pushed out, and the unreacted gas and air react on the electrode reaction surface. By being consumed, the stack voltage is quickly lowered, and the stop time can be shortened. This operation also has an effect of reducing the amount of water that is condensed by the next activation and becomes liquid water by discharging water vapor in each gas pipe.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a configuration of a first embodiment of a fuel cell system according to the present invention.
FIG. 2 is a flowchart for explaining an operation at startup in the first embodiment.
FIG. 3 is a diagram illustrating an example of a determination time t3 with respect to a stop time before activation.
FIG. 4 is a flowchart for explaining water, that is, an exclusion operation in the first embodiment.
FIG. 5 is a flowchart illustrating an emergency stop operation in the first embodiment.
FIG. 6 is a configuration diagram showing the configuration of a second embodiment of the fuel cell system according to the present invention.
FIG. 7 is a flowchart for explaining an operation at the time of activation in the second embodiment.
FIG. 8 is a configuration diagram showing the configuration of a third embodiment of the fuel cell system according to the present invention.
FIG. 9 is a flowchart illustrating a system stop operation in the third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Fuel cell stack 2 Air supply apparatus 3 Fuel supply apparatus 4 Fuel supply shut valve 5 Fuel gas supply pressure adjustment valve 6 Fuel gas circulation ejector (1st ejector)
7 Air exhaust pressure control valve 8 Purge valve 9 Air stack inlet pipe 10 Fuel gas supply pipe 11 Fuel gas stack inlet pipe 12 Air stack outlet pipe 13 Air exhaust pipe 14 Fuel gas circulation pipe 15 Fuel gas purge pipe 16 Fuel gas replacement acceleration ejector ( Second ejector)
17 Replacement promotion shut valve (first on-off valve)
18 Check valve 19 Replacement promotion pipe 20 Replacement promotion ejector drive air pipe 21 Circulation shut-off shut valve (second on-off valve)
22 Air introduction shut valve 23 Check valve 24 Control device

Claims (11)

Unreacted fuel gas discharged from the fuel electrode outlet of the fuel cell stack is supplied to the suction port of the first ejector via the fuel gas circulation pipe, and new fuel gas is supplied as a driving flow to the inlet of the first ejector. In a fuel cell system for supplying a mixed gas of a reaction fuel gas and the new fuel gas from an outlet of a first ejector to a fuel cell stack,
A second ejector is provided at the air electrode outlet of the fuel cell stack,
Connecting the fuel gas circulation pipe to the suction port of the second ejector;
A fuel cell system comprising switching means for selectively switching whether or not to use the second ejector. 2. The fuel cell system according to claim 1, wherein the switching means is a first on-off valve provided between a suction port of a second ejector and the fuel gas circulation pipe. 2. The fuel cell system according to claim 1, further comprising a second on-off valve downstream of a connection portion between the fuel gas circulation pipe and a suction port of a second ejector. It has an air exhaust pressure control valve that controls the pressure at the air electrode outlet,
The fuel cell system according to claim 1, wherein a second ejector is connected in parallel with the air exhaust pressure control valve via a check valve. A method for controlling a fuel cell system according to any one of claims 1 to 4, comprising:
A control method for a fuel cell system, wherein the switching means is switched to use a second ejector when the fuel cell system is started. 6. The method of controlling a fuel cell system according to claim 5, wherein the usage time of the second ejector is controlled according to the stop duration before starting. 6. The method of controlling a fuel cell system according to claim 5, wherein when the second ejector is used, the supply pressure of the fuel gas and air to the fuel cell stack is increased compared to when the second ejector is not used. The method for controlling a fuel cell system according to any one of claims 1 to 4, further comprising a purge valve that discharges unreacted fuel gas from the fuel gas circulation pipe to the outside.
A control method for a fuel cell system, wherein when the water clogging occurs in the fuel cell stack, the switching means is switched so that the purge valve is opened and the second ejector is used. A method for controlling a fuel cell system according to any one of claims 1 to 4, comprising:
A control method for a fuel cell system, wherein the switching means is switched to use a second ejector when power generation is stopped. An air introduction pipe connecting the fuel electrode inlet and the air electrode inlet downstream of the first ejector, and a third on-off valve for opening and closing the air introduction pipe,
10. The fuel cell system control method according to claim 9, wherein the supply of fuel gas is stopped when power generation is stopped, and the third on-off valve is opened to introduce air into the fuel pipe. The method for controlling a fuel cell system according to any one of claims 1 to 4, further comprising a purge valve that discharges unreacted fuel gas from the fuel gas circulation pipe to the outside.
A control method for a fuel cell system, wherein the purge valve is opened and the switching means is switched so as to use a second ejector when the fuel cell system is to be urgently stopped when the system is abnormal.

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